It is common knowledge that air, be it entrained or surface foam, will cause pressure ripples in hydraulic pumps, due to implosion of air bubbles. These pressure ripples can manifest themselves as objectionable audible noise, manifest as “pump whine” in some transmissions. New automatic transmissions with their compact sumps and high pump pressures have raised the possibility of consumer reaction to this issue. A number of OEMs have taken steps to reduce the air level in the fluid in their new transmissions by (1) isolating, or “baffling”, the internal rotating components to separate them from the fluid, or (2) introducing “aeration” additives into the ATF to help the oil release the entrained air more quickly or reduce the level of entrained air. Additionally, traditional ATF additive technology would include at low levels a common “antifoam” agent to help dissipate surface air bubbles.
Antifoams work in part by being insoluble in ATF. This lack of solubility, though necessary for foam reduction, can have a negative impact on the amount of antifoam that can be added to an ATF to form a stable mixture. Conventional ATFs can contain 3–10 ppm silicon contribution from the antifoam agent. For most ATF applications, this level is suitable for controlling foam. However, in modern transmissions with high pressure pumps, this level may not be adequate due to loss of antifoam activity. Conventional wisdom holds to the notion that higher levels of antifoam actually degrade air release performance by impeding entrained bubbles from releasing from the fluid. The effect of increased aeration due to high levels of antifoam is thought to be exacerbated in high pressure hydraulic applications.
U.S. Pat. No. 6,251,840 describes lubricating compositions for ATFs with decreased air entrainment. The European counterpart EP 0761805 B1 teaches a mixture of silicone and fluorosilicone antifoam agents.
U.S. Pat. No. 5,766,513 describes antifoam agents in ATFs having a polyacrylate and fluorosilicone, wherein the antifoam agents are used in very low, traditional amounts.
U.S. Pat. No. 5,372,735 describes an effective way of overcoming the shudder problem associated with the continuous slip torque converter clutches for use in automatic transmissions, especially shudder which occurs with new friction materials before break-in.
U.S. Pat. No. 5,422,023 describes lubricant compositions containing alkyl substituted dimercaptothiodiazoles together with an alpha-olefin/malic ester copolymer in a lubricating oil.
U.S. Pat. No. 4,990,273 describes an antiwear additive for lubricating compositions which is the reaction product of 2,5-dimercapto-1,3,4-thiadiazole with an aldehyde and an amine.
U.S. Pat. No. 4,612,129 describes dimercapto-thiadiazole derivatives as corrosion inhibitors used in compositions containing a metal salt of a dithiocarbamic acid and an oil soluble sulfurized organic compound.
U.S. Pat. No. 4,301,019 describes reacting mercapto-thiadiazole with hydroxyl-containing unsaturated esters, or their borated derivatives to yield products useful as friction reducing additives in lubricants.
U.S. Pat. No. 4,140,643 describes reacting an oil-soluble dispersant with a dimercapto-thiadiazole and subsequently reacting the intermediate thus formed with a carboxylic acid or anhydride.
U.S. Pat. No. 4,136,043 describes reacting an oil soluble dispersant and a dimercapto-thiadiazole at 100–250° C. until the reaction product will form a homogeneous blend with a lubricating oil.
European Patent Application publication number 0630 960 A1 discloses the use of dimercapto-thiadiazoles with a copolymer of methacrylate, methyl-methacrylate and an amine-based antioxidant.
European Patent Application publication number 0601266 A1 describes compounds prepared by reacting 2,5-dimercapto-1,3,4-thiadiazole, aldehydes, and aromatic amines and their use as antiwear and antioxidant agents in lubricating compositions.
All patents and patent applications cited herein are incorporated herein by reference in their entirety.